The present invention relates to an image reader for reading image data and an electrophotographic image forming apparatus including the image reader.
An image reader (scanner) for reading image data, which is used in an image forming apparatus, is shaped almost like a plate and includes a transparent document holding section (document glass) for holding an object to be read, such as a sheet-like document, a book and a solid object, an illuminating lamp, and a reflector. The image reader also includes an illuminating unit for illuminating the object set on the document glass, a CCD sensor for converting an image contained in the object into an electrical signal upon receiving light reflected from the object illuminated with illuminating light emitted from the illuminating unit, and an optical set (a plurality of mirrors and a focusing lens) provided between the document glass and the CCD sensor. An analog electrophotographic apparatus using an exposing mirror and a photosensitive drum in place of the CCD sensor, for directly guiding light, which is reflected from an object to be read, to the photo-sensitive drum, includes a document glass (document holding section), an illuminating unit and an optical set which are similar in structure to those of the above image reader (scanner).
In the foregoing image reader (scanner), the illuminating unit and some mirrors of the optical set are formed along and longer than the short side of the document glass, and moved at a given speed in the direction along the long side thereof perpendicular to the short side at right angles. Thus, an image to be scanned is picked up as variations of light and shade within a long irradiation range along the first direction (the short side of the document glass) defined by the illuminating light from the illuminating lamp and mirrors, and then guided onto the light-receiving surface of the CCD. When the illuminating lamp and mirrors are moved in the second direction (the long side of the document glass) crossing the first direction at right angles, the entire image of the object to be scanned is picked up as variations of light and shade and guided onto the light-receiving surface of the CCD sensor.
If the object to be scanned is a sheet-like document formed by pasting a sheet document (second sheet) on a mount sheet (first sheet), a shade is likely to occur in a boundary between the first and second sheets. The thicker the second sheet, the clearer the shade. The cause thereof is unbalanced light emitting from the illuminating unit toward the sheet-like document, the unbalanced light being a difference between the intensity of light traveling along the second direction in which the illuminating lamp and mirrors move and that of light traveling in the direction opposite to the first direction. When a difference in level between the pasted sheets occurs at an end portion of the document, a shade appears at the edge of the document when the document is illuminated. This shade can be eliminated by software if a non-scanning area is set (at the time of scanning by the scanner). However, when the second sheet is small and located in or close to the central part of the first sheet or when a small document is to be located in the central part of a large paper sheet, a shade is unlikely to be eliminated by software even though a non-scanning area is set. Furthermore, even though a specific image process can be performed to delete the shade, an image whose density is lower than that of the shade will be deleted simultaneously.
In order to improve the unbalanced light from illuminating unit, an idea of using two lamps to make the intensity of light traveling in the moving direction and that of light traveling in the direction opposite to the moving direction equal to each other, has been proposed (put to practical use). If, however, two lamps are used, the coincidence of brightness (coincidence of intensity of light from the two lamps) is required and naturally the costs are increased. To heighten the reflectivity of a reflector has also been proposed (put to practical use), however, a reflector having a high reflectivity is expensive and its loss is about 10% when it reflects the light. The brightness is therefore lower that that in the case using two lamps. Further, a method of collecting the light reflected by the reflector having a curved surface within an irradiation range, has been put to practical use, but the reflector itself increases in cost. In this case, the width of the irradiation range and that of the collected reflected light are shifted from each other, and the amount of light received by the CCD sensor is greatly varied with a mounting error of the CCD sensor.
An object of the present invention is to provide an illuminating apparatus for reading/copying an object having a portion of different thickness varies without causing any undesired image in the portion.
Another object of the present invention is to provide an image reader which causes no shade in an object having a difference in level when the object is illuminated.
Still another object of the present invention is to provide an image reader or an image forming apparatus which is capable of reading/copying an image free of shade by irradiating an object with illuminating light having almost uniform light intensity from different two directions using both of a virtual light source constituted of the reflector and an illuminating lamp.
An image reader according to a first aspect of the present invention comprises:
a holding member for holding an object to be read, the holding member being a rectangular, plate-like, flat member having two pairs of sides perpendicular to each other at right angles;
an illuminating unit, including a tube-like lamp and provided in parallel with one of the two pairs of sides of the holding member, for illuminating an area having a given range on the holding member;
a reflector, provided along the lamp of the illuminating unit, for converging the light from the object to the holding member;
a converging lens for converging the light reflected by the object on the holding member illuminated by the illuminating unit and the reflector; and
a CCD sensor for receiving the light focused by the focusing lens and outputting an electrical signal corresponding to the received light.
An image forming apparatus according to a second aspect of the present invention comprises:
a holding glass for holding an object, the holding glass being a rectangular, plate-like, flat member having a pair of long sides and a pair of short sides crossing each other at right angles;
an illuminating unit having a xenon lamp and a reflector both for illuminating the object placed on one side of the holding glass, the xenon lamp reflecting light toward an irradiation range in order to irradiate the object, and the reflector having a first reflection plane and a second reflection plane and emitting light toward the irradiation range from a direction opposite to a direction of the light emitted from the xenon lamp in order to irradiate the holding glass;
a converging lens for providing an image-forming characteristic to the light reflected by the object on the holding member illuminated by the illuminating unit; and
a CCD sensor for receiving the light to which the image-forming characteristic is provided by the converging lens, and outputting an electrical signal corresponding to the received light.
An image forming apparatus according to a third aspect of the present invention comprises:
an image reader including:
a holding glass for holding an object, the holding glass being a rectangular, plate-like, flat member having a pair of long sides and a pair of short sides crossing each other at right angles a holding glass for holding an object, the holding glass being a rectangular, plate-like, flat member having a pair of long sides and a pair of short sides crossing each other at right angles;
an illuminating unit having a xenon lamp and a reflector both for illuminating the object placed on one side of the holding glass, the xenon lamp reflecting light toward an irradiation range in order to irradiate the object, and the reflector having a first reflection plane and a second reflection plane and emitting light toward the irradiation range from a direction opposite to a direction of the light emitted from the xenon lamp in order to irradiate the holding glass;
a focusing lens for focusing the light reflected by the object on the holding member illuminated by the illuminating unit; and
a CCD sensor for receiving the light focused by the focusing lens and outputting an electrical signal corresponding to the received light;
a converging lens for providing an image-forming characteristic to the light reflected by the object on the holding member illuminated by the illuminating unit; and
a CCD sensor for receiving the light to which the image-forming characteristic is provided by the converging lens, and outputting an electrical signal corresponding to the received light;
an exposing unit for emitting exposure light, whose intensity varies with an output image signal generated from the image reader, to a predetermined position;
an image forming unit having a photo-sensitive body serving as a light acceptor, a developing unit capable of selectively supplying a visualizing material to the photo-sensitive body, and a transfer unit for transferring the visualizing material from the photo-sensitive drum to an image-transferred member, for forming a visualizing-material image by supplying the visualizing material to a latent image formed on the photo-sensitive body by the exposure light emitted from the exposing unit;
an image-transferred member feeding mechanism for feeding the image-transferred member to the transfer unit to transfer the visualizing-material member formed by the developing unit by the transfer unit of the image forming unit; and
a fixing unit for fixing the visualizing-material image on the image-transferred member fed by the image-transferred member feeding mechanism.